by JimDirt » Fri Jul 31, 2015 11:28 am
The piston should have Valve Reliefs cut into them , the LARGER is for the Intake side , the SMALLER is for the Exhaust side , make sure the Intake side is facing the REAR of the engine
At no point should the valves hit the piston , so either timing is off or the piston is very high compression , in conjunction with a cam with very high lift (aftermarket) , but something is definitely wrong , and do not try to actually start the bike till its fixed
As far as timing goes , you will have several marks that have to ALL line up at the same time , 2 are on the Ignition side 1 is on the Clutch side
The clutch side will be a large round plug in front of the clutch cover , it will have a Arrow on the case itself facing to the front of the engine , the Gear will have a dot usually , it needs to be aligned with the Arrow on the case .....
While that is in position you should also note the cam has the lobes facing rearwards about 2 o clock position when looking from the Ignition (left) side of the engine , at this position there are 2 slash marks on the gear (like this - ) , one on the rear half of the gear , the other on the front half , they both need to be level , so it will look like this (-o-)
The 3rd mark is the small round plug on the Ignition side , it will have several marks , but 1 of them should be lined up the the notch in the opening , if ALL these marks are aligned at the same time ,. then your timing is correct , if not then you will have to readjust the timing chain till they ALL align at the same time
2020 CRF450R
2006 CRF450X
Weiser , Idaho